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    CWG Issue 2452</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="2452"></A><H4>2452.
  
Flowing off the end of a coroutine
</H4>
<B>Section: </B>8.8.5&#160; [<A href="https://wg21.link/stmt.return.coroutine">stmt.return.coroutine</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD6
 &#160;&#160;&#160;

 <B>Submitter: </B>Lewis Baker
 &#160;&#160;&#160;

 <B>Date: </B>2020-02-14<BR>


<P>[Accepted at the November, 2020 meeting.]</P>

<P>There are two references to &#8220;flowing off the end of a
coroutine&#8221;, specifically in 8.8.5 [<A href="https://wg21.link/stmt.return.coroutine#3">stmt.return.coroutine</A>] paragraph 3:
</P>

<BLOCKQUOTE>

If <I>p</I><TT>.return_void()</TT> is a valid expression,
flowing off the end of a coroutine is equivalent to a
<TT>co_return</TT> with no operand; otherwise flowing off the
end of a coroutine results in undefined behavior.

</BLOCKQUOTE>

<P>and 9.6.4 [<A href="https://wg21.link/dcl.fct.def.coroutine#11">dcl.fct.def.coroutine</A>] paragraph 11:</P>

<BLOCKQUOTE>

The coroutine state is destroyed when control flows off the
end of the coroutine or...

</BLOCKQUOTE>

<P>These mean different things and should be clarified.</P>

<P><B>Proposed resolution (July, 2020):</B></P>

<P>Change 8.8.5 [<A href="https://wg21.link/stmt.return.coroutine#3">stmt.return.coroutine</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

If <I>p</I><TT>.return_void()</TT> is a valid expression,
flowing off the end of a
coroutine<INS>'s <I>function-body</I></INS> is equivalent to
a <TT>co_return</TT> with no operand;otherwise flowing off
the end of a coroutine<INS>'s <I>function-body</I></INS>
results in undefined behavior.

</BLOCKQUOTE>

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